1. Field of Art
The present invention relates to a micro electro mechanical system (MEMS) apparatus.
2. Related Art
Micro electro mechanical systems have been used in several fields. For example, MEMS-based radio frequency (RF) switches (RF-MEMS switches) offer low transmission loss and high isolation in an off-state.
FIG. 12 shows a schematic illustration of a switch with electrostatic action to turn on or off.
An RF-MEMS switch 11, shown in FIG. 12, consists of two electrodes 11a and 11b, and a movable contact 11c and fixed contacts 11d and 11e provided between the electrodes 11a and 11b. The contacts 11d and 11e are connected to input and output terminals 13 and 14, respectively.
A high potential is applied to either of the electrodes 11a and 11b whereas a low potential to the other.
A more detailed configuration of the RF-MEMS switch 11 is shown in FIGS. 13A to 13E. FIG. 13A is a plan view of the switch 11. FIG. 13B is a cross section of the switch 11 taken on line A–A′ in FIG. 13A in an open-state. FIG. 13C is a cross section of the switch 11 taken on line B–B′ in FIG. 13A in an open-state. FIG. 13D is a cross section of the switch 11 taken on line A–A′ in FIG. 13A in a closed-state. FIG. 13E is a cross section of the switch 11 taken on line B–B′ in FIG. 13A in a closed-state.
As shown in FIGS. 13A to 13E, the electrode 11b is fixed on a substrate 30 whereas the electrode 11a is fixed on a cantilever 20 having an anchor 20a fixed on the substrate 30.
The movable contact 11c is provided at an end of the cantilever 20, opposite to the other end at which the anchor 20a is provided. The fixed contacts 11d and 11e are provided on the substrate 30.
No voltages to the electrodes 11a and 11b keep the cantilever 20 in an up-state position, as shown in FIGS. 13B and 13C, so that the movable contact 11c does not touch the fixed contacts 11d and 11e, thus RF-MEMS switch 11 is in an open-state.
Contrary to this, a certain voltage across the electrodes 11a and 11b generates an electrostatic force to shift the cantilever 20 in a down-state position, as shown in FIGS. 13D and 13E, so that the movable contact 11c touch the fixed contacts 11d and 11e, thus RF-MEMS switch 11 is brought in a closed-state.
One possible application of capacitive RF-MEMS switches such as explained above is a mobile communications device thanks to low transmission loss and high isolation in an off (open)-state.
Capacitive RF-MEMS switches, however, require a drive voltage in the range from several ten to several hundred volts to give a large spring constant to a movable constant for avoiding contact between the movable constant and fixed contacts to achieve high reliability.
Accordingly, installation of such a capacitive RF-MEMS switch in a mobile communications device powered by a several-volt battery requires a boosted battery voltage or a lower drive voltage to the switch.
A lower drive voltage, however, causes lower reliability of capacitive RF-MEMS switches.
Integration of a power IC with a capacitive RF-MEMS switch, for giving a high drive voltage to the switch, could generate noises that affect the switch.